ATP Finals: Nadal withdraws due to knee injury .
Nadal was defeated by Belgium's first-time qualifier David Goffin with the score of 7-6, 6-7, 6-4, before announcing his decision to discontinue the competition, reported the Independent .
"I'm not ready to play . I fought a lot knowing it was my last match of the season," Nadal said .
Nadal tried hard to score the second set of the match against Goffin but began to struggle with his movement in the third .
After losing the match to Goffin, Nadal in his post-match press interview confirmed his withdrawal . (ANI)